Sarah, one of the patients depicted in Undocumented: Healthcare for the Hidden at Four Corners Film Gallery, E2, to 10 Sep.
Photograph: Mark Sherratt

Build a wall … A great wall. But will it be high enough, big enough, thick enough? Will it be Trump-size, visible from space? Will it keep out the undesirables ? Will it protect the lorry drivers and nervous holidaymakers? Will it look nice if we put a few plants around it? Are the French going to raze the Jungle to the ground just as they did Sangatte?

I do not know whether Robert Goodwill, the immigration minister who announced the grand folly of a £1.9m wall in Calais – “We’ve done the fences, now we are doing a wall” – has a clue what he is talking about but this is part of a £17m security package that “we” are partaking in with the French to tackle the problem of the camp in Calais. This is the ultimate in closed thinking.

Walls, barriers, boundaries, borders, blockades: these are structures that make us feel in control, but in the end remind us only of chaos. This is part of the Brexit mentality, part but not all. There is another part that means opening up to a world beyond Europe and righteous Remainers should be wary of constructing even more walls around their own arguments, which seem to outdo each other in convincing us that everything will be terrible for ever.

The result of this on the left – except among those with a vivid enough imagination to actually envisage Jeremy Corbyn shambling down the G20 red carpet in China – is political paralysis. No more pessimism of the intellect, optimism of the will, but pessimism about everything. This a truly dangerous place to be. I understand the feeling: the world is going to hell in a handcart, so there is nothing to be done. It is a form of paralysis solved only by moving to places where nothing ever happens: New Zealand, Canada … Failing that, we make little walls around ourselves. Cosy up as the nights draw in and try not to think. About anything.

Strangely, though, the best cure for such a feeling is the opposite. It is getting involved with people who do work to change the lives of others, who make movement possible, whose very work is to pull down barriers not erect them.

This was made clear to me by Undocumented, an exhibition celebrating 10 years of a Bethnal Green clinic run by Doctors of the World which is used by migrants locked out of the healthcare system. In reality, everyone in the UK should be able to access healthcare. One of the myths is that this is what people come here for. The reality is that, if you are homeless and don’t have a national insurance number, you can’t access it.

Sarah (pictured above) explained this to me. She is from South Africa where she had been “correctionally” raped. Men, she said, had come to “fix” her because of her sexuality. She became pregnant and HIV positive. She could not get a GP but the clinic helped her. And there she was, beaming in front of photographs of herself despite her horrific story.

Ibrahim, a former Doctors of the World service user who is now training to practise as UK GP. Photograph: Toby Coulson

A man, Ibrahim Muyhayer, who was a doctor in the Sudanese army but had to leave because of the political volatility, told me how it had taken him five years to access the system. He was charged £2,000 for an ultrasound scan for his pregnant wife though he was earning £50 a week. Now he volunteers in the clinic and is retraining to practise as a doctor here.

This basic ethos of treating medical need, whatever the patient’s immigration status, is what this charity does. This is why it also runs clinics in Calais and works with refugees in Greece.

Users of the clinic often carry stories of awful suffering, torture, loss and rape, but this is the only service providing primary healthcare. Tearing down the barriers. It was the same in Calais. Unlike the immigration minister, I have been to the camps. It would take him an hour to get there. It’s incredible that he has not. Anyone who has actually talked to anyone in the Jungle, or worse, in Grande-Synthe, the camp in Dunkirk, would smell the desperation. Every night, these people risk getting their hands ripped up, breaking their limbs and getting teargassed trying to get over the fences because they feel that they have no life anyway. They will get around a wall.

So this wall is a symbolic gesture to be built with taxpayers’ money. That money could surely be used to fund centres for the processing of asylum claims. But something unforgivable is happening when we cannot even let in the unaccompanied children from the camps. Stella Creasy, MP for Walthamstow, went over with Alf Dubs to try and do something about this. Those kids, with their strange “protectors” lurking behind them, haunt me. These are traumatised children, left to rot and be exploited. The volunteers do the best they can, but the situation is at breaking point.

Nevertheless, to hear the stories of those who have been helped, is to be jolted out of political ennui. Lives can be rebuilt.

A wall is sign of a failure of humanity. In 1964, the artist Joseph Beuys satirised the Berlin wall, suggesting it be raised by 5cm to have better proportions. He made his point and we know what happened to that wall. It is good to be reminded that there are those who build walls but there are those who will build ladders over them. That is called hope.